FIELD OF THE INVENTION
Oil Pollution Caused By Oil Spills
The growth of environmental consciousness combined with an ever-increasing use of petroleum products has led to a heightened awareness of the need promptly and effectively to remediate pollution caused by various petroleum-based activities. In addition, the diminishing production of domestic petroleum has caused an ever-expanding reliance upon foreign-produced oil. Except for Mexican and Canadian oil delivered by pipeline, all foreign oil must be delivered by ocean transport. Even Alaskan oil enters the continental United States by oil tanker. Despite increased governmental oversight and regulation, navigation over the oceans is inherently risky. Unpredictable weather, increased ocean traffic, mechanical defects, and negligence or intentional acts all contribute to the release of significant quantities of crude oil and petroleum products onto oceans, seas, bays, estuaries, and other waterways. In addition to vessel accidents, such discharges have been caused by warfare, illegal flushing of vessels' holds, offshore oil drilling and production platform accidents.
Oil contamination has produced severe environmental harm, as in coastal Alaska, resulting in mounting public and legislature concern. Oil spills are now recognized to result in extensive ecological and economic damage by destroying aquatic life, by fouling municipal water intakes, recreational beaches, boats, fish and harbors, and by interfering with a wide variety of aquatic recreational activities.
Methods of Remediating Oil Spills
Along with this increasing consciousness of the seriousness of the consequences of oil spills has come an increasing dissatisfaction with the traditional methods of cleaning spilled oil from oceans and bays. In former times, burning of the spilled oil was a preferred remedy. Such burning was always difficult to accomplish because of the natural difficulty of burning anything so closely associated with water as are oil spills. Burning also causes extensive air pollution, the Kuwait fires being only one example of how climate can be effected by such burning. In addition, burning is extremely dangerous, and can produce grave hazards to those engaged in remediation using such a technique.
Two other traditional methods of oil clean-up have also recently become less acceptable. One method is to allow micro-organisms and chemical processes to degrade petroleum molecules into relatively harmless substances ("bio-remediation"). Another is to disperse the oil using the natural aids of weather and time, sometimes accelerated by the use of "dispersion aids" such as surfactants or soaps. These techniques are today considered as essentially equivalent to doing nothing. They are also now recognized to have severe limitations. Bio-remediation is such a slow process that much harm is usually caused before significant degradation occurs. Chemical dispersion does not remove oil, but rather spreads it more widely over a larger aquatic area, and hence brings it more closely into contact with both marine life and aquatic birds. The oil's particle size distribution becomes smaller while its geographic distribution increases. If the spill occurred in a coastal environment, the oil is likely to contact the shore, where it will cause unsightly conditions and unacceptable harm.
Using "sinking" chemicals, which cause spilled oil to increase its specific gravity so that it is out of sight under water is also very much out of style. Sinking has been determined to have uniquely detrimental side effects. Most importantly, it retards degradation of oil by aerobic bacteria, and incorporates it into underwater sediment, where it can be preserved for long periods of time, where it will prove toxic to benthic organisms. Areas near shore particularly have high levels of biological activity as evidenced by the presence of shrimp, shellfish, clams, crabs, mollusks and food fish. These valuable forms of life can be wiped out or harmed by introducing oil into their fragile habitations. Since a large number of oil spills occur close to shore, sinking is of limited application.
Oil Spill Treating Agents
The art has developed at least four classes of oil spill treating agents; solidifiers, demulsifying agents, surface-washing agents and dispersants. Several treating agent products in each of these categories have been offered to the marketplace.
Solidifiers or gelling agents solidify oil. Typically such agents require between 5% and 100% of agent by weight compared to the oil. De-emulsifying agents or emulsion breakers prevent the formation of or break water-in-oil emulsions. Surfactant-containing materials are of two types, surface-washing agents and dispersants. Of known surface washing agents, only a few agents have effectiveness of greater than 25%, where this is defined as the percentage of oil removed from a test surface. Dispersant effectiveness results have been reported-heavy oils show effectiveness values of about 1%, medium crudes of about 10%, light crude oils of about 30% and very light oils of about 90%. Many surface washing agents have been sold in the Noah American market with most, however, not still commercially available.
A number of agents which have been sold for various purposes, but do not cleanly fit into the above categories, include those that help trace or detect oil, those which are combinations of the categories described above, and those very esoteric items that are claimed to make oil disappear, or become non-toxic, for example.
It is estimated that scores of oil spill treating agents have been promoted at one time or another on the World market. This high number of products have caused difficulties to the potential remediator-customer, and even to environmentalists because such customer is often unable to discriminate between those products which will actually help the situation and those which are ineffective (and even cause further dispersion and damage).
Effectiveness has remained the major problem with most treating agents. Effectiveness is generally a function of oil type and composition. Crude and refined oil products have a wide range of molecular sizes and compositions including whole categories of materials like asphaltenes, alkanes, aromatics and resins. What is often effective for small asphaltene compounds in an oil may be ineffective on large asphaltenes. A treating agent for an aromatic compound may not be effective on a polar compound. Other major factors in agent effectiveness are environmental parameters such as low temperature and high sea energy. The effects of both oil composition and environmental parameters must be determined to establish the actual utility of a spill treating agent. A brief discussion of the different type of agents is instructive.
a) Solidifiers or Gelling Agents
Solidifiers are those agents which change oil from liquid to solid. Commercial agents often consist of polymerization catalysts and cross-linking agents. Agents which are actually sorbents are not generally considered to be gelling agents. Most such agents function, but required large amounts of agent to effectively solidify the oil. Under some situations the oil became a viscous thixotropic semi-solid which does not really aid in recovery. Because of the large amount of agent required, gelling agents have not been historically used nor stocked for use by spill remediators. PA1 Several known prior art agents are available to break or prevent emulsions. Most agents are hydrophilic surfactants; that is, surfactants with a strong tendency to make oil-in-water emulsions. Such surfactants have the ability to revert the water-in-oil emulsion into two separate phases. A hydrophilic surfactant is more soluble in water than in oil and, for this reason, will quickly leave the oil. Such products are generally not useable on open water. There are at least two common uses for de-emulsifiers, one on the open seas to break or prevent the formation of emulsions, and in tanks to break recovered emulsions. PA1 Common oil spill treating agents are those containing surfactants as the major ingredient. These agents have been divided into two groups, dispersants and surface-washing agents. Dispersants are those agents which have approximately the same solubility in water and oil and cause the oil to be dispersed into the water in the form of fine droplets. Surface-washing agents are those agents which remove oil from solid surfaces such as beaches by the mechanism known as detergency. A product which is a good surface-washing agent is usually a poor dispersant and vice versa. Low dispersant effectiveness is a benefit for any product that will be used as a surface washing agent because oil can then be recovered rather than dispersed into the water column. Furthermore, because the two properties of surface-washing and dispersancy are at cross-purposes, highly effective products do not have a significant dispersant effectiveness. Many products display neither property adequately.
b) De-Emulsifiers or Emulsion Breakers
c) Surface-Washing Agents and Dispersants
In this specification, the term oil spill means the physical presence of an oil or an oil-product floating on fresh or salt water. Although the bulk of the applications are on high seas, they are also useful for applications involving tanks, streams, harbors and sewage-treatment facilities.
Physical Removal of Oil Spills in Cold Water Environments
Actual physical removal (for example by "skimming" or pumping operations) is today ecologically the most preferred remedy for oil remediation. However, using prior art technologies, skimming has been found to be useful only under nearly ideal weather, water turbulence and response time conditions. Where ocean waves are high, more turbulent than normal, where winds or ocean currents are in excess of a few knots, where low and freezing temperatures exist, or where the periods of daylight are limited (as in northern waters in the winter), physical removal operations are likely to be ineffective, delayed, and extremely costly. More importantly, areas having consistently cold air and water temperatures, such as Alaska, the Arctic Ocean, the northern Atlantic Ocean, and the North Sea, make existing methods normally useless, even when seas are calm. Since oil spills often occur in such cold climates, the art has long looked to a product and a process for oil spill removal that would be "all-weather effective" as well as cost-efficient.
If a physical removal process is to be effective, the oil spill must be agglomerated and gathered together into a confined space on the water surface, for a sufficient period of time to permit removal or treatment operations. For the remediation of ocean oil spills, an agglomeration process and additive must possess two important physical properties: (1) it must provide good cold temperature solidification of oil, and (2) it must allow sustained buoyancy in salt or fresh water for the confined oil. The solidification of the oil is important so that it does not disperse over vast areas of ocean, magnifying the clean-up problem. It is very important that any product and process be able to solidify oil at low temperatures (0.degree. C.) as well as at high temperatures (40.degree.-45.degree. C.), which would make the product universally effective for use in cold Arctic waters as well as tropical waters. Buoyancy of the additive is important as well, since it is necessary to keep the additive on the surface of the water to allow sufficient mixing time with the oil, and then to allow for collection of the agglomeration. Oil agglomeration is desirable because it aids in the physical gathering of the spilled oil. Proper agglomeration of this kind should produce relatively large patches of viscous oil instead of the normally--occurring very thin films of oil on the water's surface. This agglomeration action is brought about by mechanical and chemical action of the additive used upon the spilled oil.